Method for localised repair of a damaged thermal barrier

Abstract

A method of localized repair to a damaged thermal barrier, the method including subjecting a part coated in a damaged thermal barrier to electrophoresis treatment, the part being made of an electrically conductive material, the damaged thermal barrier including a ceramic material and presenting at least one damaged zone that is to be repaired, the part being present in an electrolyte including a suspension of particles in a liquid medium, the ceramic coating being deposited by electrophoresis in the damaged zone in order to obtain a repaired thermal barrier for use at temperatures higher than or equal to 1000° C., the particles being made of a material different from the ceramic material present in the damaged thermal barrier.

Claims

1. A method of localized repair to a damaged thermal barrier, the method comprising: a) subjecting a part coated by a damaged thermal barrier to electrophoresis treatment, the part being made of an electrically conductive material, the damaged thermal barrier comprising a ceramic material and having a columnar structure, the damaged thermal barrier presenting at least one damaged zone that is to be repaired, the part being present in an electrolyte comprising a suspension of particles in a liquid medium, the particles in a non-agglomerated state having a mean size lying in the range from 20 nm to 1 μm, a ceramic coating being deposited by electrophoresis in the damaged zone in order to obtain a repaired thermal barrier for use at temperatures higher than or equal to 1000° C., the particles being made of a material different from the ceramic material present in the damaged thermal barrier, wherein prior to step a), the method includes a step of forming the particles by performing a sol-gel method, said sol-gel method comprising a supercritical drying of a liquid precursor to form the particles.

2. A method according to claim 1, wherein before the beginning of step a), the particles are present in the liquid medium at a concentration greater than or equal to 0.1 g/L.

3. A method according to claim 1, wherein the duration of step a) is greater than or equal to 1 minute.

4. A method according to claim 1, wherein a voltage greater than or equal to 1 V is imposed during all or part of step a) between the part and a counter electrode.

5. A method according to claim 1, wherein a thickness e of the deposited ceramic coating is greater than or equal to 30 μm.

6. A method according to claim 1, wherein the part is coated by an attachment layer enabling the thermal barrier to attach to the part, and wherein the ceramic coating is deposited on the attachment layer.

7. A method according to claim 1, wherein prior to step a), the damaged zone is subjected to a stripping step.

8. A method according to claim 1, wherein after step a), the method includes a step b) of consolidation by subjecting the deposited ceramic coating to heat treatment.

9. A method according to claim 1, wherein the part constitutes a turbine engine blade.

10. A method of localized repair to a damaged thermal barrier, the method comprising: a) subjecting a part coated by a damaged thermal barrier to electrophoresis treatment, the part being made of an electrically conductive material, the damaged thermal barrier comprising a ceramic material and having a columnar structure, the damaged thermal barrier presenting at least one damaged zone that is to be repaired, the part being present in an electrolyte comprising a suspension of particles in a liquid medium, the particles in a non-agglomerated state having a mean size lying in the range from 20 nm to 1 μm, a ceramic coating being deposited by electrophoresis in the damaged zone in order to obtain a repaired thermal barrier for use at temperatures higher than or equal to 1000° C., the particles being made of a material different from the ceramic material present in the damaged thermal barrier, wherein a generator imposes a potential difference between the part and a counter electrode during the electrophoresis treatment, the generator generating a pulsed current during the electrophoresis treatment.

11. A method according to claim 10, wherein before the beginning of step a), the particles are present in the liquid medium at a concentration greater than or equal to 0.1 g/L.

12. A method according to claim 10, wherein the duration of step a) is greater than or equal to 1 minute.

13. A method according to claim 10, wherein a voltage greater than or equal to 1 V is imposed during all or part of step a) between the part and a counter electrode.

14. A method according to claim 10, wherein a thickness e of the deposited ceramic coating is greater than or equal to 30 μm.

15. A method according to claim 10, wherein the part is coated by an attachment layer enabling the thermal barrier to attach to the part, and wherein the ceramic coating is deposited on the attachment layer.

16. A method according to claim 10, wherein prior to step a), the damaged zone is subjected to a stripping step.

17. A method according to claim 10, wherein after step a), the method includes a step b) of consolidation by subjecting the deposited ceramic coating to heat treatment.

18. A method according to claim 10, wherein the part constitutes a turbine engine blade.

19. A method according to claim 10, wherein the counter electrode is made of platinum.

20. A method of claim 10, wherein the ceramic coating being deposited by electrophoresis in the damaged zone covers an entire surface of the damaged zone.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other characteristics and advantages of the invention appear from the following description given with reference to the accompanying drawings, in which:

(2) FIG. 1 is a photograph of a turbine engine blade damaged in service;

(3) FIG. 2 comprises a photograph of a turbine engine blade damaged in service together with a fragmentary diagram illustrating the structure of the damaged thermal barrier;

(4) FIGS. 3A and 3B show, in diagrammatic and fragmentary manner, the performance of a method of the invention; and

(5) FIGS. 4A and 4B are photographs showing a part respectively before and after treatment by a method of the invention.

DETAILED DESCRIPTION OF IMPLEMENTATIONS

(6) FIG. 2 shows a part 1, e.g. made of a nickel-based superalloy, coated by an adhesion layer 2 having a damaged thermal barrier 3 present thereon. An oxide layer 2a is present between the adhesion layer 2 and the damaged thermal barrier 3. The layer 2a may be made of α-Al.sub.2O.sub.3 alumina. The damaged thermal barrier 3 comprises a ceramic material and it presents a damaged zone 4 that is to be repaired.

(7) The damaged zone 4 may present at least one adjacent zone that is not damaged. In the example shown, the damaged zone 4 is present between two adjacent zones 5a 5b that are not damaged.

(8) FIG. 3A shows the implementation of a step a) of the invention. As shown, the part 1 carrying the damaged thermal barrier 3 is present in an electrolyte 10 comprising a suspension of particles 11 in a liquid medium. By way of example, the particles 11 may be particles of yttria-stabilized zirconia (zirconia stabilized by yttrium oxide).

(9) By way of example, there follows a description of the steps of sol-gel synthesis of an yttria-stabilized zirconia powder for use, in one implementation, in forming the particles 11: mixing acetyl acetone in 1-propanol and zirconium propoxide (Zr(OC.sub.3H.sub.7).sub.4); mixing the resulting mixture with a solution of yttrium nitrate in 1-propanol; mixing the resulting mixture with water and with 1-propanol (10 moles per liter (mol/L)) in order to obtain a sol; stoving the sol at a temperature of 50° C.; evaporative drying or supercritical drying; and calcination in air at a temperature of 700° C.

(10) The oxide powder (yttria-stabilized zirconia) as obtained in this way is then put into suspension in a liquid medium, e.g. constituted by isopropanol in order to form the electrolyte 10.

(11) The part 1 coated by the damaged thermal barrier 3 constitutes one electrode of the electrophoresis system, and it has a counter electrode 20 placed facing it. By way of example, the counter electrode 20 is made of platinum. Because of the conductive nature of the part 1 and of the damaged zone 4, deposition by electrophoresis takes place in the damaged zone 4. In the example shown, the damaged zone 4 is constituted by a region lacking material. In a variant that is not shown, the damaged zone comprises a first region that is lacking in material together with a second region in which a ceramic layer is present, the thickness of the ceramic layer present in the second region being small enough for the second region to be electrically conductive. In another variant, the damaged zone comprises a region in which a ceramic layer is present, the thickness of the ceramic layer being small enough for this region to be electrically conductive.

(12) Deposition takes place preferentially in the most conductive zones (ceramic layer of sufficiently small thickness or total absence of ceramic layer) since the electric field is relatively high in such zones.

(13) An implementation is shown in which the damaged thermal barrier 3 presents a single damaged zone 4 that is to be repaired, but it would not go beyond the ambit of the present invention for the damaged thermal barrier to present a plurality of damaged zones that are to be repaired. Under such circumstances, each of the damaged zones to be repaired is electrically conductive.

(14) During step a), a generator G imposes a potential difference between the part 1 and the counter electrode 20. The generator G generates direct current (DC) or pulses. The part 1 is biased with a charge opposite to the charge of the particles 11. As a result of an electric field being applied between the part 1 and the counter electrode 20, the particles 11 move and become deposited on the part 1 in order to form a ceramic coating 6. Depositing the ceramic coating 6 in the damaged zone 4 enables a repaired thermal barrier 7 to be obtained. Depositing the ceramic coating 6 in the damaged zone 4 progressively reduces the electrical conductivity of this zone over time. Specifically, as the ceramic coating 6 continues to be deposited, this zone becomes more and more insulating, thereby slowing down or even stopping the formation of the ceramic coating 6 on the part 1.

(15) As shown, the ceramic coating 6 is deposited in the damaged zone 4 and covers the entire surface of the damaged zone 4.

(16) Advantageously, while the ceramic coating 6 is being deposited, the damaged thermal barrier 3 is not covered in a mask presenting an opening overlying the damaged zone 4 that is to be repaired. Also, there is no need before the step a) to remove a portion of the damaged thermal barrier 3 situated outside the damaged zone 4 that is to be repaired.

(17) The ceramic coating 6 may present thickness e that is greater than or equal to 50 nm, e.g. greater than or equal to 30 μm. The thickness e of the ceramic coating 6 corresponds to its greatest dimension as measured perpendicularly to the surface S of the coated part 1.

(18) After step a), it is possible to subject the ceramic coating 6 to drying followed by consolidation heat treatment.

EXAMPLE

(19) Use was made of a nickel-based superalloy part coated by an yttria-stabilized zirconia (YSZ) thermal barrier obtained by electron beam physical vapor deposition (ED-PVD). The thermal barrier was initially damaged by water jet. FIG. 4A shows the result obtained after damaging.

(20) Electrophoresis deposition was performed using a suspension of YSZ powder in isopropanol (10 g/L) at a voltage of 100 V for six minutes. A photograph of the part after treatment by the method of the invention is shown in FIG. 4B.

(21) It can be seen that a covering and uniform deposit of yttria-stabilized zirconia is obtained throughout the damaged zone.

(22) The term “comprising/containing a/an” should be understood as “comprising/containing at least one”

(23) The term “lying in the range . . . to . . . ” should be understood as including the limits of the range.